Bacillus anthracis infection is primarily a disease of cattle, but humans can acquire the infection following contact with infected animal products or soil (Mourez et al. Trends Microbiol. 10:287, 2002). Despite the relatively low numbers of naturally occurring infections in the U.S. (Jernigan et al., Emerg. Infect. Dis. 7:933, 2001), Bacillus anthracis is a deadly and efficient bioterrorism agent, as demonstrated by the anthrax attacks in late 2001. Efforts are underway to develop and to stockpile therapeutics for the treatment of established anthrax infection to confront this serious threat to public health (Fox, Nat. Biotechnol. 21:216, 2003). To this end, anthrax toxin components have been used as therapeutic targets (Greenfield and Bronze, Curr. Opin. Investig. Drugs 5:135, 2004), as these bacterial proteins are virulence factors for Bacillus anthracis. These toxin components include lethal factor (LF), edema factor (EF), and protective antigen (PA). Anthrax PA forms pores in cells, thereby permitting intracellular transport of the active toxin enzymes, EF and LF.
Technical challenges currently reduce the ability to identify anthrax therapeutics. For example, in vivo efficacy testing is currently performed in animal models of anthrax infection, due to the low national incidence of naturally-occurring anthrax infection in humans (Chang et al., Emerg. Infect. Dis. 9:556, 2003). However, in vitro assays for anthrax toxin activity are needed that closely reflect the in vivo effects of the toxin during human infection. Although in vitro assays are currently available for measuring anthrax LT activity, such assays are limited because they are based on the species- and strain-specific action of the toxin to lyse and/or to inhibit proliferation of BALB/c-derived murine macrophage lines (Hering et al., Biologicals 32:17, 2004). These cytotoxic actions of anthrax LT that are cell-, strain-, and species-specific have not been demonstrated to occur in human cells.
Therefore, there is a need for bioassays based on human cell parameters that can be used to screen for agents that reduce anthrax LT activity.